This invention relates to electromagnetic clutches and, in particular, to such clutches which are adaptable, for use in controlling the transmission of an automobile engine output to refrigerant compressors for automobile air conditioning refrigerating systems.
In U.S. Pat. Nos. 3,044,594 and 3,082,933, electromagnetic clutches are disclosed which are used between the engine and the compressor for selectively driving the compressor. The shown electromagnetic clutch comprises a pulley which is mounted on a bearing mounted on a tubular extension of a compressor housing and which is rotated by a belt from the automobile's engine. The pulley is provided with a plurality of concentric annular magnetic pole faces at an axial end thereof. A drive shaft of the compressor extends through the tubular extension. A hub is fixed to the extending terminal end of the drive shaft, and an annular armature plate is joined by leaf springs to the hub in such fashion that the armature plate faces the annular concentric pole faces with space therebetween. A magnetic coil is mounted on the tubular extension to supply magnetic flux for attracting the armature plate to the magnetic pole faces.
Thus, when the magnetic coil is energized, the drive shaft is rotated together with the pulley by the engine output, and when the magnetic coil is not energized, the pulley is rotated by the engine but the compressor is not driven.
In the above described known clutches, the transmission of the rotating force from the pulley to the shaft is effected by the friction at the contacting surface between the pulley and the armature plate. Therefore, it is required that the contacting friction between the pulley and the armature be quite large. This requires a larger coil, greater electrical energy, an increase of poles of the pulley and the armature plate, and/or the use of complicated structures in the contacting surfaces of the pulley and armature.